Conventionally, there are electric punch presses using a servo motor as a driving source of a ram. In punching working of a press machine such as a punch press, since extremely large noise is generated during the working, it is required to decrease this kind of noise as small as possible.
Principles of generation of noise in the punching working are complicated, and reasons of generation of noise are varied depending upon various conditions such as the material of the work, the plate thickness, and the like. However, it is known that the noise is large when the punching speed by driving of a ram is fast, the noise becomes smaller when the punching speed becomes slower, and when the punching speed is constant, the noise is small when the load is light, and as the load becomes heavier, the noise becomes larger.
The above conventional technique is disclosed in Japanese Patent Applications Laid-Open Nos. 2001-62591 and 2001-62596.
However, the conventional electric punch press generates a torque necessary for working by using a mechanism such as a toggle and a flywheel. Therefore, the inertia caused by this mechanism delays the reciprocating motion of the ram. In addition, an operation shaft which vertically moves the ram and a main shaft of a servo motor is driven through a power transmission mechanism such as a gear, and a loss or a delay is generated by the power transmission mechanism. Even if the speed of the servo motor is controlled, the driving speed of the ram can not follow the speed of the servo motor easily, and therefore the conventional technique is not suitable for controlling the speed of the ram.
For this reason, the conventional technique has problems that since the punching speed is set substantially at a constant value irrespective of the weight of the load, if the punching speed is set lower to decrease the noise, the operation efficiency is largely deteriorated, and if the punching speed is set higher to enhance the operation efficiency, a large noise is generated and thus, reduction of noise and enhancement of operation efficiency can not be satisfied at the same time.
According to the conventional system, a predetermined punching pattern is switched in a hydraulic press system depending upon the plate thickness, material, and the like to satisfy both the noise reduction and increase of punching speed. Therefore, complicated control systems such as high-speed processing hardware and software are required.
Generally, there are a hydraulic punch press using hydraulic pressure as the driving source of the ram and an electric punch press using a servo motor. In the punch press, the same punching die such as a nibble is used and a work is continuously punched in some cases. In such a continuous punching working, a speedup of the ram is required.
In the conventional hydraulic punch press, however, since the ram is reciprocated using a hydraulic pressure and a switching valve, response speed is inferior to that of the electric control, and a response delay to the control command is generated and thus, the conventional hydraulic punch press is not suitable for speedup of the ram.
Further, the conventional technique has problems that since the punching speed is set substantially at a constant value irrespective of the weight of the load, if the punching speed is set lower to decrease the noise, the operation efficiency is largely deteriorated, and if the punching speed is set higher to enhance the operation efficiency, a large noise is generated and thus, reduction of noise and enhancement of operation efficiency can not be satisfied at the same time.
It is assumed herein to drive the operation shaft which vertically moves the ram, directly by the servo motor without through a power transmission mechanism such as a gear and without using a mechanism such as a toggle and a flywheel. If the operation shaft is driven directly by the servo motor, there is a possibility that the punching speed can automatically be increased or decreased according to the load, and with this, there is a possibility that both the noise reduction and the enhancement of operation efficiency can be satisfied at the same time.
If a case where a mechanism such as a toggle and a flywheel is used for generating a torque necessary for the working and a case where the mechanism is not used (direct driving by the servo motor) are compared with each other, in the punching working using the punch press, since a large punching energy is required at the time of the punching working in addition to the kinetic energy for vertically moving the ram at high speed, a servo motor having a greater rating is required in the direct driving.
In order to drive the operation shaft which vertically moves the ram directly by the servo motor, it is necessary to supply, to the servo motor, electric energy for high speed operation and for punching working, and a peak electricity of a control circuit for the servo motor becomes extremely high.
The present invention has been achieved in order to solve the conventional problems, and it is a first object of the present invention to eliminate the conventional problems, and to provide a servo drive system of a press machine which can decrease a noise by automatically increasing and decreasing the punching speed according to a load without using a mechanism such as a toggle and a flywheel, and without using a power transmission mechanism such as a gear, and which can prevent mechanical portions corresponding to one side of the operation shaft from being distorted, and realize stabilized operation.
It is a second object of the present invention to eliminate the conventional problems, and to provide a servo drive system of a press machine which can decrease a noise and enhance the operation efficiency at the same time by automatically increasing and decreasing the punching speed according to a load.
It is a third object of the present invention to eliminate the conventional problems, and to provide a continuous working system of a press machine in which transmission of a driving force is not delayed in principle, control delay is not generated, responding speed is high, and operation speed is high, while using a servo motor as a driving source of a ram without using a mechanism such as a toggle and a flywheel and a power transmission mechanism such as a gear.
It is a fourth object of the present invention to eliminate the conventional problems, and to provide a servo drive system of a punch press which can decrease a noise and enhance the operation efficiency at the same time by automatically increasing and decreasing the punching speed according to a load, and reduce a peak electricity of a control circuit for the servo motor.